Composite carbonate and method for producing the same

ABSTRACT

The present invention provides a nickel atom-, manganese atom- and cobalt atom-containing composite carbonate that is high in specific surface area and large in tap density, and useful as a raw material for producing a lithium nickel manganese cobalt composite oxide to be used in a positive electrode active material for use in a lithium secondary battery, and provides a method for industrially advantageously producing the composite carbonate. The composite carbonate includes nickel atoms, manganese atoms and cobalt atoms, and has an average particle size of 5 μm or more and less than 20 μm, a BET specific surface area of 40 to 80 m 2 /g and a tap density of 1.7 g/ml or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composite carbonate useful as a rawmaterial for producing a lithium nickel manganese cobalt composite oxideto be used in a positive electrode active material for use in a lithiumsecondary battery and a method for producing the composite carbonate.

2. Description of the Related Art

Lithium cobaltate has hitherto been used as a positive electrode activematerial for a lithium secondary battery. However, lithium nickelmanganese cobalt composite oxides low in cobalt content have beendeveloped because cobalt is a rare metal.

In these years, there have been demanded batteries excellent in rapidcharge properties to be used in electric automobiles and power toolssuch as electric tools. Although increase of the specific surface areaof the positive electrode material is a technique to cope with rapidcharge, lithium nickel manganese cobalt composite oxides having hithertobeen developed are all small in specific surface area.

Most of conventional methods for synthesizing lithium nickel manganesecobalt composite oxides use as starting raw materials nickel manganesecobalt composite hydroxides; the raw materials are small in specificsurface area, and consequently, lithium nickel manganese cobaltcomposite oxides obtained therefrom are also small in specific surfacearea.

On the other hand, methods using as starting raw materials nickelmanganese cobalt composite carbonates have also been proposed. Proposedexamples of the method for producing a nickel manganese cobalt compositecarbonate include the following two methods: the method of JapanesePatent Laid-Open No. 2001-148249 (p. 7, p. 9) (Patent Document 1) inwhich a solution that contains sulfates of nickel, manganese and cobaltand an aqueous solution that contains ammonium bicarbonate aresimultaneously or alternately added dropwise to a water-containingsolution to conduct the reaction while the pH of the solution is beingcontrolled to fall within a range from 6.5 to 8.5; and the method ofJapanese Patent Laid-Open No. 2006-117517 (p. 7) (Patent Document 2) inwhich a solution that contains sulfates of nickel, manganese and cobaltand an aqueous solution that contains sodium carbonate aresimultaneously added to a water-containing solution to conduct thereaction.

However, the composite carbonates obtained by the production methodsdisclosed in above-described Patent Documents 1 and 2 are 40 m²/g ormore in the BET specific surface area as the case may be but are assmall as less than 1.7 g/ml in tap density, and accordingly suffers froma problem that the lithium composite oxide produced by using thecomposite carbonate gives a low filling density of the positiveelectrode active material in an electrode fabricated with the compositecarbonate. Thus, there has been demanded development of a nickel atom-,manganese atom- and cobalt atom-containing composite carbonate that ishigh in specific surface area and large in tap density, and useful as araw material for producing a lithium nickel manganese cobalt compositeoxide to be used in a positive electrode active material for use in alithium secondary battery.

Accordingly, an object of the present invention is to provide a nickelatom-, manganese atom- and cobalt atom-containing composite carbonatethat is high in specific surface area and large in tap density, anduseful as a raw material for producing a lithium nickel manganese cobaltcomposite oxide to be used in a positive electrode active material foruse in a lithium secondary battery, and to provide a method forindustrially advantageously producing the composite carbonate.

SUMMARY OF THE INVENTION

In view of the above-described circumstances, the present inventorsdiligently conducted a great deal of study, and consequently, perfectedthe present invention by discovering that: when a composite carbonate isobtained by conducting a reaction by adding a solution (solution A) thatcontains a nickel salt, a manganese salt and a cobalt salt and asolution (solution B) that contains a metal carbonate or a metalhydrogen carbonate to a solution (solution C) that contains the sameanions as the anions of the nickel salt, the manganese salt and thecobalt salt in the solution A and the same anion as the anion of themetal carbonate or the metal hydrogen carbonate in the solution B, thecomposite carbonate is higher both in specific surface area and in tapdensity than conventional composite carbonates, and additionally has aspecific average particle size; the lithium nickel manganese cobaltcomposite oxide obtained by using the thus obtained composite carbonateas the raw material for producing the composite oxide is high both inspecific surface area and in tap density; and a lithium secondarybattery that uses the composite oxide as the positive electrode activematerial exhibits excellent battery performance.

Specifically, an aspect (1) of the present invention is the provision ofa composite carbonate, wherein the composite carbonate includes nickelatoms, manganese atoms and cobalt atoms, and has an average particlesize of 5 μm or more and less than 20 μm, a BET specific surface area of40 to 80 m²/g and a tap density of 1.7 g/ml or more.

Additionally, an aspect (2) of the present invention is the provision ofa method for producing a composite carbonate, wherein the compositecarbonate is obtained by conducting a reaction by adding a solution(solution A) that contains a nickel salt, a manganese salt and a cobaltsalt and a solution (solution B) that contains a metal carbonate or ametal hydrogen carbonate to a solution (solution C) that contains thesame anions as the anions of the nickel salt, the manganese salt and thecobalt salt in the solution A and the same anion as the anion of themetal carbonate or the metal hydrogen carbonate in the solution B.

According to the present invention, there can be provided a nickelatom-, manganese atom- and cobalt atom-containing composite carbonatethat is high in specific surface area and large in tap density, anduseful as a raw material for producing a lithium nickel manganese cobaltcomposite oxide to be used in a positive electrode active material foruse in a lithium secondary battery, and there can be provided a methodfor industrially advantageously producing the composite carbonate.Additionally, a lithium nickel manganese cobalt composite oxide highboth in specific surface area and in tap density can be obtained byusing the composite carbonate of the present invention as a raw materialfor producing the composite oxide. Yet additionally, a lithium secondarybattery that uses the composite oxide as a positive electrode activematerial exhibits excellent battery performance, in particular,excellent load property.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an electron micrograph of a composite carbonate obtained inExample 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention is described on the basis of thepreferred embodiments thereof.

The composite carbonate of the present invention is a compositecarbonate that contains nickel atoms, manganese atoms and cobalt atoms,and has an average particle size of 5 μm or more and less than 20 μm, aBET specific surface area of 40 to 80 m²/g and a tap density of 1.7 g/mlor more.

The composite carbonate of the present invention is a compositecarbonate that contains nickel atoms, manganese atoms and cobalt atoms.In the composite carbonate of the present invention, the ratio of thecontent of the nickel atoms to the content of the manganese atoms is, interms of the molar ratio of the nickel atom content to the manganeseatom content (Ni:Mn), preferably 1:0.5 to 2.0, particularly preferably1:0.9 to 1.1 and further preferably 1:0.95 to 1.05. Also in thecomposite carbonate of the present invention, the ratio of the contentof the nickel atoms to the content of the cobalt atoms is, in terms ofthe molar ratio of the nickel atom content to the cobalt atom content(Ni:Co), preferably 1:0.5 to 2.0, particularly preferably 1:0.9 to 1.1and further preferably 1:0.95 to 1.05. When the ratio of the content ofthe manganese atoms to the content of the nickel atoms is less than theabove-described range, the content of manganese that is an element lowin price becomes low to tend to be uneconomical, and on the other hand,when exceeds the above-described range, the tap density tends to be low.Also when ratio of the content of the cobalt atoms to the content of thenickel atoms is less than the above-described range, the tap densitytends to be low, and on the other hand, when exceeds the above-describedrange, the content of high price cobalt becomes large to tend to beuneconomical.

The average particle size of the composite carbonate of the presentinvention is 1 μm or more and less than 20 μm and preferably 5 to 15 μmin terms of the average particle size obtained by a laser particle sizedistribution measurement method.

One of the features of the composite carbonate of the present inventionis the high specific surface area thereof. Specifically, the BETspecific surface area of the composite carbonate of the presentinvention is 40 to m²/g and preferably 50 to 80 m²/g. The BET specificsurface area of the composite carbonate of the present invention fallingwithin the above-described range yields a lithium nickel manganesecobalt composite oxide high in specific surface area, and consequentlyenables to improve the battery performance, in particular, the loadproperty of a lithium secondary battery.

The tap density of the composite carbonate of the present invention is1.7 g/ml or more and preferably 1.7 to 2.2 g/ml. The tap density of thecomposite carbonate of the present invention falling within theabove-described range yields a lithium nickel manganese cobalt compositeoxide high in tap density, hence makes excellent the filling property ofthe composite oxide, and consequently enables to improve the batteryperformance, in particular, the volume energy density of a lithiumsecondary battery, and additionally enables the mass production of alithium nickel manganese cobalt composite oxide.

It is to be noted that the tap density as referred to in the presentinvention is defined as a value derived by a tap method on the basis ofthe apparent density or apparent specific volume method described inJIS-K-5101 as follows: 5 g of a sample is placed in a 5-ml graduatedcylinder, tapped 500 times and allowed to stand still, then the volumeof the sample is read off and the tap density is derived from thefollowing calculation formula:Tap density (g/ml)=F/Vwherein F represents the mass (g) of the treated sample in the graduatedcylinder and V represents the volume (ml) of the sample after tapping.

Next, the method for producing a composite carbonate of the presentinvention is described. The method for producing a composite carbonateof the present invention is a method for producing a composite carbonatewherein the composite carbonate is obtained by conducting a reaction byadding a solution (solution A) that contains a nickel salt, a manganesesalt and a cobalt salt and a solution (solution B) that contains a metalcarbonate or a metal hydrogen carbonate to a solution (solution C) thatcontains the same anions as the anions of the nickel salt, the manganesesalt and the cobalt salt in the solution A and the same anion as theanion of the metal carbonate or the metal hydrogen carbonate in thesolution B.

In other words, the method for producing a composite carbonate of thepresent invention is a method for producing a composite carbonatewherein the nickel atom-, manganese atom- and cobalt atom-containingcomposite carbonate is obtained by conducting the reaction by adding thesolution A and the solution B to the solution C.

The solution A involved in the method for producing a compositecarbonate of the present invention is a solution that contains a nickelsalt involved in the solution A, a manganese salt involved in thesolution A and a cobalt salt involved in the solution A.

The nickel salt involved in the solution A is not particularly limitedas long as the nickel salt is water-soluble to yield a nickelion-containing aqueous solution; examples of the nickel salt include thesulfate salt, the chloride salt, the nitrate salt and the acetate saltof nickel. Additionally, the manganese salt involved in the solution Ais not particularly limited as long as the manganese salt iswater-soluble to yield a manganese ion-containing aqueous solution;examples of the manganese salt include the sulfate salt, the chloridesalt, the nitrate salt and the acetate salt of manganese. Additionally,the cobalt salt involved in the solution A is not particularly limitedas long as the cobalt salt is water-soluble to yield a cobaltion-containing aqueous solution; examples of the cobalt salt include thesulfate salt, the chloride salt, the nitrate salt and the acetate saltof cobalt. Among these salts, the sulfate salts and the chloride saltsare preferable because of being economical. In the solution A, thenickel salt involved in the solution A may include two or more types ofnickel salts different in anion from each other, the manganese saltinvolved in the solution A may include two or more types of manganesesalts different in anion from each other, and the cobalt salt involvedin the solution A may include two or more types of cobalt saltsdifferent in anion from each other. Additionally, in the solution A, theanion of the nickel salt involved in the solution A, the anion of themanganese salt involved in the solution A and the anion of the cobaltsalt involved in the solution A may be the same or different from eachother.

The solution A is obtained by dissolving in water, for example, thenickel salt involved in the solution A, the manganese salt involved inthe solution A and the cobalt salt involved in the solution A. In otherwords, the solution A is an aqueous solution of the nickel salt involvedin the solution A, the manganese salt involved in the solution A and thecobalt salt involved in the solution A. The solution A may contain theimpurities contained in the nickel salt involved in the solution A, themanganese salt involved in the solution A and the cobalt salt involvedin the solution A, and may contain other metal salts as long as theother metal salts do not adversely affect the advantageous effects ofthe present invention.

In the solution A, the content of nickel ions in terms of nickel atom ispreferably 0.1 to 2.0 mol/L and particularly preferably 0.5 to 2.0mol/L, the content of manganese ions in terms of manganese atom ispreferably 0.1 to 2.0 mol/L and particularly preferably 0.5 to 2.0mol/L, and the content of cobalt ions in terms of cobalt atom ispreferably 0.1 to 2.0 mol/L and particularly preferably 0.5 to 2.0mol/L. The contents of the nickel ions, the manganese ions and thecobalt ions in the solution A respectively falling within theabove-described ranges enable to reduce the amount of the waste solutionleft after the reaction preferably from the viewpoint of beingindustrially advantageous.

Additionally, in the solution A, the ratio of the content of the nickelions to the content of the manganese ions is, in terms of the molarratio of the nickel atom content to the manganese atom content (Ni:Mn),preferably 1:0.5 to 2.0, particularly preferably 1:0.9 to 1.1 andfurther preferably 1:0.95 to 1.05. Also in the solution A, the ratio ofthe content of the nickel ions to the content of the cobalt ions is, interms of the molar ratio of the nickel atom content to the cobalt atomcontent (Ni:Co), preferably 1:0.5 to 2.0, particularly preferably 1:0.9to 1.1 and further preferably 1:0.95 to 1.05. The molar ratio in thesolution A between the nickel atom content, manganese atom content andcobalt atom content falling within the above-described range furtherenhances the effects to increase the specific surface area and the tapdensity of the composite carbonate.

On the other hand, in the solution A, the total content of the anion ofthe nickel salt involved in the solution A, the anion of the manganesesalt involved in the solution A and the anion of the cobalt saltinvolved in the solution A is preferably 0.3 to 12 mol/L andparticularly preferably 1.5 to 12 mol/L although the total content isvaried depending on the types of the metal salts.

The solution B involved in the method for producing a compositecarbonate of the present invention is a solution that contains any oneor both of the metal carbonate involved in the solution B and the metalhydrogen carbonate involved in the solution B.

The metal carbonate involved in the solution B is not particularlylimited as long as the metal carbonate is water-soluble to yield acarbonate ion-containing aqueous solution; examples of the metalcarbonate include: alkali metal carbonates such as sodium carbonate andpotassium carbonate; and ammonium carbonate. The metal hydrogencarbonate involved in the solution B is not particularly limited as longas the metal hydrogen carbonate is water-soluble to yield a hydrogencarbonate ion-containing aqueous solution; examples of the metalhydrogen carbonate include: alkali metal hydrogen carbonates such assodium hydrogen carbonate and potassium hydrogen carbonate; and ammoniumhydrogen carbonate. Preferable among these is sodium hydrogen carbonatebecause sodium hydrogen carbonate does not contain ammonia, renders thepH of the reaction solution nearly neutral and is low in price. In thesolution B, the metal carbonate involved in the solution B may includetwo or more types of metal carbonates different in cation from eachother, and the metal hydrogen carbonate involved in the solution B mayinclude two or more types of metal hydrogen carbonates different incation from each other. Additionally, in the solution B, when thesolution B contains the metal carbonate involved in the solution B andthe metal hydrogen carbonate involved in the solution B, the cation ofthe metal carbonate involved in the solution B and the cation of themetal hydrogen carbonate involved in the solution B may be the same ordifferent from each other.

The solution B is obtained by dissolving in water, for example, any oneor both of the metal carbonate involved in the solution B and the metalhydrogen carbonate involved in the solution B. In other words, thesolution B is an aqueous solution of any one or both of the metalcarbonate involved in the solution B and the metal hydrogen carbonateinvolved in the solution B. The solution B may contain the impuritiescontained in the metal carbonate involved in the solution B or the metalhydrogen carbonate involved in the solution B, and may contain othermetal salts as long as the other metal salts do not adversely affect theadvantageous effects of the present invention.

In the solution B, the content of carbonate ions or hydrogen carbonateions (the total content of carbonate ions and hydrogen carbonate ionswhen the solution B contains both of the metal carbonate involved in thesolution B and the metal hydrogen carbonate involved in the solution B),in terms of CO₃, is preferably 0.1 to 2.0 mol/L and particularlypreferably 0.5 to 2.0 mol/L. The content of the carbonate ions or thehydrogen carbonate ions in the solution B falling within theabove-described range enable to reduce the amount of the waste solutionleft after the reaction preferably from the viewpoint of beingindustrially advantageous.

On the other hand, in the solution B, the content of the cation of themetal carbonate involved in the solution B or the cation of the metalhydrogen carbonate involved in the solution B (the total content of thecation of the metal carbonate involved in the solution B and the cationof the metal hydrogen carbonate involved in the solution B when thesolution B contains both of the metal carbonate involved in the solutionB and the metal hydrogen carbonate involved in the solution B), in termsof the metal atom of the cation, is preferably 0.1 to 2.0 mol/L andparticularly preferably 0.5 to 2.0 mol/L although the cation content isvaried depending on the type(s) of the metal salt(s).

The solution C involved in the method for producing a compositecarbonate of the present invention is a solution that contains “the sameanions as the anions of the nickel salt, the manganese salt and thecobalt salt contained in the solution A involved in the method forproducing a composite carbonate of the present invention” and “the sameanion as the anion of the metal carbonate or the metal hydrogencarbonate contained in the solution B involved in the method forproducing a composite carbonate of the present invention.”

The solution C is obtained by dissolving in water, for example, “a metalsalt that contains the following same anion when the anion of the nickelsalt, the anion of the manganese salt and the anion of the cobalt saltcontained in the solution A are the same and that does not react withthe anion of the metal carbonate or the metal hydrogen carbonatecontained in the solution B” and “a metal salt that contains the anionof the metal carbonate or the metal hydrogen carbonate contained in thesolution B.” Alternatively, the solution C is obtained by dissolving inwater, for example, “a plurality of metal salts that containrespectively the following individual anions when the anion of thenickel salt, the anion of the manganese salt and the anion of the cobaltsalt contained in the solution A are different from each other and thatdo not react with the anion of the metal carbonate or the metal hydrogencarbonate contained in the solution B” and “a metal salt that containsthe anion of the metal carbonate or the metal hydrogen carbonatecontained in the solution B.”

(i) For example, when the solution A contains a nickel salt, a manganesesalt and a cobalt salt all containing the same anion and the solution Bcontains any one of a metal carbonate and a metal hydrogen carbonate,specifically, when the solution A contains nickel chloride, manganesechloride and cobalt chloride, and the solution B contains sodiumhydrogen carbonate, then the solution C contains chloride ion andhydrogen carbonate ion. In this case, the solution C is obtained bydissolving in water, for example, a metal salt such as sodium chloridethat has the same anion as the anion of nickel chloride, manganesechloride and cobalt chloride contained in the solution A and that doesnot react with sodium hydrogen carbonate contained in the solution B anda metal salt such as sodium hydrogen carbonate that has the same anionas the anion of sodium hydrogen carbonate contained in the solution B.

(ii) Additionally, when the solution A contains a nickel salt, amanganese salt and a cobalt salt different in anion from each other andthe solution B contains any one of a metal carbonate and a metalhydrogen carbonate, specifically, when the solution A contains nickelchloride, manganese sulfate and cobalt nitrate and the solution Bcontains sodium carbonate, then the solution C contains chloride ion,sulfate ion, nitrate ion and carbonate ion. In this case, the solution Cis obtained by dissolving in water, for example, a plurality of metalsalts such as sodium chloride, sodium sulfate and sodium nitrate thathave the respective anions of nickel chloride, manganese sulfate andcobalt nitrate contained in the solution A and that do not react withthe sodium carbonate contained in the solution B and a metal salt suchas sodium carbonate that has the same anion as the anion of sodiumcarbonate contained in the solution B.

(iii) Still additionally, when the solution A contains a nickel salt, amanganese salt and a cobalt salt all having the same anion and thesolution B contains both of a metal carbonate and a metal hydrogencarbonate, specifically, when the solution A contains nickel chloride,manganese chloride and cobalt chloride and the solution B containssodium carbonate and sodium hydrogen carbonate, then the solution Ccontains chloride ion, carbonate ion and hydrogen carbonate ion. In thiscase, the solution C is obtained by dissolving in water, for example, ametal salt such as potassium chloride that has the same anion as theanions of nickel chloride, manganese chloride and cobalt chloridecontained in the solution A and that does not react with the sodiumcarbonate and sodium hydrogen carbonate contained in the solution B andmetal salts such as potassium carbonate and sodium hydrogen carbonatethat have respectively the same anions as the anions of sodium carbonateand sodium hydrogen carbonate contained in the solution B.

(iv) Yet additionally, when the solution A contains a nickel salt, amanganese salt and a cobalt salt different in anion from each other andthe solution B contains both of a metal carbonate and a metal hydrogencarbonate, specifically, when the solution A contains nickel chloride,manganese sulfate and cobalt nitrate and the solution B contains sodiumcarbonate and potassium hydrogen carbonate, then the solution C containschloride ion, sulfate ion, nitrate ion, carbonate ion and hydrogencarbonate ion. In this case, the solution C is obtained by dissolving inwater, for example, a plurality of metal salts such as sodium chloride,potassium sulfate and potassium nitrate that have the respective anionsof nickel chloride, manganese sulfate and cobalt nitrate contained inthe solution A and that do not react with the sodium carbonate andpotassium hydrogen carbonate contained in the solution B and metal saltssuch as potassium carbonate and sodium hydrogen carbonate that haverespectively the same anions as the anions of sodium carbonate andpotassium hydrogen carbonate contained in the solution B.

The inclusion, in the solution C, of the same anion(s) as the anion(s)of the nickel salt, manganese salt and cobalt salt contained in thesolution A and the same anion as the anion of the metal carbonate or themetal hydrogen carbonate contained in the solution B enables to reducethe change of the anion component in the solution under reaction, henceenables to simultaneously increase the specific surface area and the tapdensity of the composite carbonate, and additionally enables to stablyproduce the composite carbonate of the present invention.

It is to be noted that the solution C may contain the impuritiescontained in the metal salts used in the preparation of the solution C,and may contain other metal salts as long as the other metal salts donot adversely affect the advantageous effects of the present invention.

In the solution C, the total content of “the same anion(s) as theanion(s) in the nickel salt, manganese salt and cobalt salt contained inthe solution A” and “the same anion as the anion of the metal carbonateor the metal hydrogen carbonate contained in the solution B” is, interms of the anion component, preferably 0.1 to 2.0 mol/L andparticularly preferably 0.5 to 1.5 mol/L, and the ratio (Y/X) of “thecontent (Y) of the same anion(s) as the anion(s) of the nickel salt,manganese salt and cobalt salt contained in the solution A” to “thecontent (X) of the same anion as the anion of the metal carbonate or themetal hydrogen carbonate contained in the solution B” is preferably 0.1to 2.0 and particularly preferably 0.5 to 1.5. The total content of “thesame anion(s) as the anion(s) in the nickel salt, manganese salt andcobalt salt contained in the solution A” and “the same anion as theanion of the metal carbonate or the metal hydrogen carbonate containedin the solution B” falling in the above-described range and the ratio(Y/X) of “the content (Y) of the same anion(s) as the anion(s) of thenickel salt, manganese salt and cobalt salt contained in the solution A”to “the content (X) of the same anion as the anion of the metalcarbonate or the metal hydrogen carbonate contained in the solution B”falling within the above-described range enable the anion concentrationof the reaction solution to always fall within a certain range and henceenable to yield a composite carbonate high both in specific surface areaand in tap density with a satisfactory yield. It is to be noted that theabove-described contents of the anions in the solution C are all givenin number of moles in terms of anions.

The condition that the solution C is a solution that contains the samecation as the cation of the metal carbonate or the metal hydrogencarbonate contained in the solution B is preferable because such acondition makes invariable the cation component in the solution underreaction and yields a composite carbonate high both in tap density andin specific surface area. In this case, the solution C can be preparedby selecting in the preparation of the solution C a metal salt that iscomposed of the same anion as the anion of the nickel salt, manganesesalt and cobalt salt contained in the solution A and the same cation asthe cation of the metal carbonate or the metal hydrogen carbonatecontained in the solution B.

When the solution C is a solution that contains the same cation as thecation of the metal carbonate or the metal hydrogen carbonate containedin the solution B, the content of the same cation in the solution C asthe cation of the metal carbonate or the metal hydrogen carbonatecontained in the solution B is, in terms of the metal atom of thecation, preferably 0.1 to 2.0 mol/L and particularly preferably 0.5 to1.5 mol/L. The content of the same cation in the solution C as thecation of the metal carbonate or the metal hydrogen carbonate containedin the solution B falling within the above-described range facilitatesthe preparation of a composite carbonate in which the ratio between thecontents of the nickel atoms, manganese atoms and cobalt atoms is, interms of the molar ratio between the nickel atoms, manganese atoms andcobalt atoms, preferably 1:0.9 to 1.1:0.9 to 1.1 and particularlypreferably 1:0.95 to 1.05:0.95 to 1.05.

The amount of the solution A added to the solution C and the amount ofthe solution B added to the solution C are such that the ratio (CO₃/M)of the total number of moles (CO₃) in terms of CO₃ of the carbonate ionand the hydrogen carbonate ion in the reaction solution to the totalnumber of moles (M) of the nickel ions, manganese ions and cobalt ionsadded from the solution A to the solution C is preferably 2 to 7 andparticularly preferably 3 to 6. The amount of the solution A added tothe solution C and the amount of the solution B added to the solution Cfalling within the above-described ranges always ensures the presence ofa sufficient amount of (CO₃) in the reaction solution in relation to thenickel ions, manganese ions and cobalt ions added from the solution A tothe solution C and hence enables to yield a composite carbonate with ahigh yield. It is to be noted that the total number of moles in terms ofCO₃ of the carbonate ion and the hydrogen carbonate ion in the reactionsolution means the total number of moles in terms of CO₃ of thecarbonate ion and the hydrogen carbonate ion originally contained in thesolution C and the carbonate ion and the hydrogen carbonate ion addedfrom the solution B to the solution C.

In the method for producing a composite carbonate of the presentinvention, the solution A and the solution B may be simultaneously oralternately added to the solution C; the solution A and the solution Bare usually added to the solution C while the solution C is beingmaintained at 10 to 90° C. and preferably at 20 to 80° C. The solution Aand the solution B are added preferably over a period of 0.5 hour ormore and particularly preferably over a period of 1 hour or more;additionally, it is preferable to add the solution A and the solution Bat a constant rate in such a way that the addition rate is controlled tomake constant the ratio between the total number of moles (M) of thenickel ions, manganese ions and cobalt ions added from the solution A tothe solution C and the total number of moles in terms of CO₃ of thecarbonate ion and the hydrogen carbonate ion in the reaction solutionbecause a composite carbonate stable in quality can be obtained in thisway. It is preferable to add the solution A and the solution B understirring. The stirring rate is only required to be such that the slurrythat contains the composite carbonate produced over a period from thestart of the addition to the end of the reaction is always in acondition to exhibit fluidity, without being particularly limitedotherwise.

After completion of the addition of the solution A and the solution B tothe solution C, solid-liquid separation is conducted in the usual mannerto yield a solid product. The thus obtained solid product is collectedand where necessary, washed with water, dried, pulverized and classifiedto yield the composite carbonate of the present invention.

The composite carbonate thus obtained by applying the method forproducing a composite carbonate of the present invention includes nickelatoms, manganese atoms and cobalt atoms, and has an average particlesize of 5 μm or more and less than 20 μm, preferably 5 to 15 μm, a BETspecific surface area of 40 to 80 m²/g, preferably 50 to 80 m²/g, and atap density of 1.7 g/ml or more, preferably 1.7 to 2.2 g/ml.Additionally, the molar ratio between the contents of the nickel atoms,the manganese atoms and the cobalt atoms in the composite carbonate ispreferably 1:0.5 to 2.0:0.5 to 2.0, preferably 1:0.9 to 1.1:0.9 to 1.1and particularly preferably 1:0.95 to 1.05:0.95 to 1.05.

The composite carbonate of the present invention is particularly usefulas a raw material for producing a lithium nickel manganese cobaltcomposite oxide to be used as a positive electrode active material of alithium secondary battery. Particularly preferable is a lithium nickelmanganese cobalt composite oxide represented by the following generalformula (1):Li_(x)Ni_(1-y-z)Mn_(y)Co_(z)O₂  (1)wherein x satisfies 0.9≦x≦1.3, y satisfies 0<y<1.0, preferably0.45≦y≦0.55, and z satisfies 0<z<1.0, preferably 0.45≦z≦0.55.

The lithium nickel manganese cobalt composite oxide represented by theabove-described general formula (1) is produced by mixing the compositecarbonate of the present invention with a lithium compound and by bakingthe thus obtained homogeneous mixture. Specifically, examples of thelithium compound include lithium carbonate and lithium hydroxide. Theaddition amount of the lithium compound is such that the ratio (Li/M) ofthe number of moles of the lithium atoms in the lithium compound to thetotal number of moles (M) of the nickel atoms, manganese atoms andcobalt atoms included in the composite carbonate is 0.8 to 1.3 andpreferably 0.9 to 1.1. The baking conditions are such that the bakingtemperature is 500 to 1100° C., preferably 650 to 850° C. and the bakingtime is 2 hours or more, preferably 3 to 12 hours. The baking atmosphereis not particularly limited; the baking may be conducted in theatmosphere or in an oxygen atmosphere. It is to be noted that when rawmaterials to produce water are baked, the baking is preferably conductedin the atmosphere or in an oxygen atmosphere as a multiple-stage baking;preferably, the baking is conducted slowly within a temperature rangefrom about 200 to 400° C. ensuring the removal of the water contained inthe raw materials, preferably over a period of 1 to 10 hours, andthereafter, the baked material is rapidly heated to 650 to 850° C. to bebaked further for 1 to 30 hours.

Additionally, the baking may be repeated unlimited times wherenecessary. Alternatively, for the purpose of ensuring uniform powderproperties, a once baked material may be pulverized to be baked again.

After baking, by appropriately cooling, and by pulverizing andclassifying where necessary, there can be obtained a lithium nickelmanganese cobalt composite oxide that has a BET specific surface area ashigh as 5 m²/g or more and a tap density as high as 1.7 g/ml or more.Such a lithium nickel manganese cobalt composite oxide is suitably usedas a positive electrode active material of a lithium secondary battery.

EXAMPLES

Hereinafter, the present invention is described in detail with referenceto Examples. However, the present invention is not limited to theseExamples.

Example 1 Preparation of Solution A

In purified water, 12.3 g (0.052 mol) of nickel chloride hexahydrate,10.3 g (0.052 mol) of manganese chloride tetrahydrate and 12.3 g (0.052mol) of cobalt chloride hexahydrate were dissolved, and then thesolution thus obtained was further diluted with purified water to 58 mlto prepare the solution A.

Preparation of Solution B

In purified water, 68 g (0.81 mol) of sodium hydrogen carbonate wasdissolved, and the solution thus obtained was further diluted withpurified water to 850 ml to prepare the solution B.

Preparation of Solution C

In purified water, 0.42 g (0.0072 mol) of sodium chloride and 0.89 g(0.011 mol) of sodium hydrogen carbonate were dissolved, and thesolution thus obtained was further diluted with purified water to 20 mlto prepare the solution C.

The compositions of these solutions were as follows.

Solution A: Ni: 0.90 mol/L, Mn: 0.90 mol/L, Co: 0.90 mol/L, Cl: 5.38mol/L

Solution B: CO₃: 0.95 mol/L, Na: 0.95 mol/L

Solution C: CO₃: 0.53 mol/L, Cl: 0.36 mol/L, Na: 0.89 mol/L

In a reaction vessel, the total amount of the solution C was placed, thesolution temperature was maintained at 80° C., and the total amount ofthe solution A and the total amount of the solution B weresimultaneously added dropwise at a constant rate to the solution C understirring at 1200 rpm over a period of 8 hours.

After the completion of the dropwise addition, solid-liquid separationwas conducted in the usual manner, and the collected product was driedat 50° C. for 12 hours and lightly pulverized to yield 18.3 g of apowder product (yield: 99%). The thus obtained powder product wassubjected to an XRD measurement and an ICP measurement to reveal thatthe powder product was a composite carbonate that contained nickel,manganese and cobalt in a molar ratio of 1.00:0.99:0.98.

Example 2

The same solutions A, B and C as in Example 1 were prepared. Then, thetotal amount of the solution C was placed in a reaction vessel, thesolution temperature was maintained at 80° C., and the total amount ofthe solution A and the total amount of the solution B weresimultaneously added dropwise at a constant rate to the solution C understirring at 2400 rpm over a period of 3.5 hours.

After the completion of the dropwise addition, solid-liquid separationwas conducted in the usual manner, and the collected product was driedat 50° C. for 12 hours and lightly pulverized to yield 18.0 g of apowder product (yield: 98%). The thus obtained powder product wassubjected to an XRD measurement and an ICP measurement to reveal thatthe powder product was a composite carbonate that contained nickel,manganese and cobalt in a molar ratio of 1.00:1.02:1.00.

Comparative Example 1

A solution prepared as follows was used as a solution D: in purifiedwater, 0.89 g (0.011 mol) of sodium hydrogen carbonate was dissolved andthe solution thus obtained was further diluted to 20 ml to prepare theconcerned solution. Otherwise, the same solutions A and B as in Example1 were prepared.

The compositions of these solutions were as follows.

Solution A: Ni: 0.90 mol/L, Mn: 0.90 mol/L, Co: 0.90 mol/L, Cl: 5.38mol/L

Solution B: CO₃: 0.95 mol/L, Na: 0.95 mol/L

Solution D: CO₃: 0.53 mol/L, Na: 0.53 mol/L

In a reaction vessel, the total amount of the solution D was placed, thesolution temperature was maintained at 80° C., and the total amount ofthe solution A and the total amount of the solution B weresimultaneously added dropwise at a constant rate to the solution D understirring at 1200 rpm over a period of 8 hours.

After the completion of the dropwise addition, solid-liquid separationwas conducted in the usual manner, and the collected product was driedat 50° C. for 12 hours and lightly pulverized to yield 17.0 g of apowder product (yield: 93%). The thus obtained powder product wassubjected to an XRD measurement and an ICP measurement to reveal thatthe powder product was a composite carbonate that contained nickel,manganese and cobalt in a molar ratio of 1.00:1.00:0.96.

Comparative Example 2

The solutions were prepared in the same manner as in Example 1 exceptthat 20 ml of purified water was adopted as the solution D.

The compositions of these solutions were as follows.

Solution A: Ni: 0.90 mol/L, Mn: 0.90 mol/L, Co: 0.90 mol/L, Cl: 5.38mol/L

Solution B: CO₃: 0.95 mol/L, Na: 0.95 mol/L

Solution D: Purified water

In a reaction vessel, the total amount of the solution D was placed, thesolution temperature was maintained at 80° C., and the total amount ofthe solution A and the total amount of the solution B weresimultaneously added dropwise at a constant rate to the solution D understirring at 1200 rpm over a period of 8 hours.

After the completion of the dropwise addition, solid-liquid separationwas conducted in the usual manner, and the collected product was driedat 50° C. for 12 hours and lightly pulverized to yield 17.7 g of apowder product (yield: 96%). The thus obtained powder product wassubjected to an XRD measurement and an ICP measurement to reveal thatthe powder product was a composite carbonate that contained nickel,manganese and cobalt in a molar ratio of 1.00:1.01:0.98.

Comparative Example 3

In purified water, 60.0 g of nickel sulfate, 117.0 g of manganesesulfate and 64.5 g of cobalt sulfate were dissolved in such a way thatthe molar ratio Ni:Mn:Co was 0.20:0.60:0.20, and the volume of thesolution was set at 500 mL (solution A). Separately, in purified water,107.5 g of ammonium bicarbonate was dissolved, and the solution thusobtained was diluted with an aqueous solution prepared by dissolving83.5 mL of concentrated aqueous ammonia in purified water to prepare a500 mL of solution (solution B).

Next, in an about 3-L stirring reaction vessel, 75 mL of spare water(solution D) was placed, and heated so as to reach 43° C. Whilecontinuously heating, the solution A and the solution B were alternatelyadded in the reaction vessel respectively with metering pumps at ratesof a few milliliters/min over a period of about 10 hours. Aftercompletion of the addition of these reaction solutions, the reactionmixture was retained for about 1 hour under stirring to promote furthercrystal growth. Thereafter, the deposited precipitate was filtered off,washed with water, and then dried for 24 hours to yield 85.7 g of apowder product (yield: 64%). The thus obtained powder product wassubjected to an XRD measurement and an ICP measurement to reveal thatthe powder product was a composite carbonate that contained nickel,manganese and cobalt in a molar ratio of 1.00:17.14:4.27.

Comparative Example 4

In 300 mL of purified water (solution D) set at a temperature of 50° C.,400 mL of a mixed aqueous solution (solution A) of nickel sulfate,manganese sulfate and cobalt sulfate (0.4 mol respectively in terms ofnickel ion, manganese ion and cobalt ion) and 500 mL of an aqueoussolution (solution B) of sodium carbonate (1.6 mol in terms of carbonateion) were added parallel under stirring over a period of 6 hours whilethe temperature was being maintained, and the reaction mixture wasneutralized. Then, the deposited precipitate was filtered off and washedto yield 163 g of a powder product (yield: 115%). The thus obtainedpowder product was subjected to an XRD measurement and an ICPmeasurement to reveal that the powder product was a composite carbonatethat contained nickel, manganese and cobalt in a molar ratio of1.00:0.97:0.97.

<Evaluation of Physical Properties>

For each of the composite carbonates obtained in Examples 1 to 3 andComparative Examples 1 to 3, the average particle size, the BET specificsurface area, the tap density and the sphericity were measured, and theresults thus obtained are shown in Table 1.

(1) Average Particle Size

The average particle size was obtained by a laser particle sizedistribution measurement method.

(2) Tap Density

The tap density was obtained on the basis of the apparent density orapparent specific volume method described in JIS-K-5101 as follows: 5 gof a sample was placed in a 5-ml graduated cylinder, the graduatedcylinder was set in an automated tap density analyzer (Dual Autotap,manufactured by Yuasa Ionics Co., Ltd.), the sample was tapped 500 timesand then the volume of the sample was measured to derive the apparentdensity as the tap density.

(3) Electron Microscope Observation

An electron micrograph of the composite carbonate obtained in Example 1is shown in FIG. 1.

TABLE 1 BET Average specific Composition ratio particle surface Tap(mol) size area density Ni Mn Co (μm) (m²/g) (g/ml) Example 1 1.00 0.990.98 10.0 58.1 1.85 Example 2 1.00 1.02 1.00 6.2 50.4 1.72 Comparative1.00 1.00 0.96 4.6 96.6 1.41 Example 1 Comparative 1.00 1.01 0.98 4.858.4 1.45 Example 2 Comparative 1.00 17.14 4.27 7.7 40.0 1.65 Example 3Comparative 1.00 0.97 0.97 4.5 187.9 1.02 Example 4

Examples 3 and 4

The composite carbonates obtained in Examples 1 and 2 and lithiumcarbonate (average particle size: 4.5 μm) were weighed out in such a waythat the ratio (Li/M) of the number of moles of the lithium atoms inlithium carbonate to the total number of moles (M) of the nickel atoms,manganese atoms and cobalt atoms in each of the composite carbonates was1.03, and each of the composite carbonates was mixed with lithiumcarbonate sufficiently with a mixer; thus homogeneous mixtures wereobtained.

Next, each of the thus obtained mixtures was baked at 800° C. for 10hours in the atmosphere, then cooled, thereafter pulverized andclassified to yield a lithium nickel manganese cobalt composite oxide.The physical properties of each of the thus obtained lithium nickelmanganese cobalt composite oxides were measured in the same manner asdescribed above, and the results thus obtained are shown in Table 2.

Comparative Example 5

A commercially offered composite hydroxide that contained nickel atoms,manganese atoms and cobalt atoms in a molar ratio of 1.00:1.01:0.98, andhas an average particle size of 10.9 μm, a BET specific surface area of6.6 m²/g and a tap density of 2.09 g/ml and lithium carbonate (averageparticle size: 4.5 μm) were weighed out in such a way that the ratio(Li/M) of the number of moles of the lithium atoms in lithium carbonateto the total number of moles (M) of the nickel atoms, manganese atomsand cobalt atoms in the composite hydroxide was 1.03, and the compositehydroxide was mixed with lithium carbonate sufficiently with a mixer;thus homogeneous mixture was obtained.

Next, the thus obtained mixture was baked at 800° C. for 10 hours in theatmosphere, then cooled, thereafter pulverized and classified to yield alithium nickel manganese cobalt composite oxide. The physical propertiesof the thus obtained lithium nickel manganese cobalt composite oxidewere measured in the same manner as described above, and the resultsthus obtained are shown in Table 2.

TABLE 2 Type of BET Ni—Mn—Co specific raw Average surface Tap materialparticle area density used size (μm) (m²/g) (g/ml) Example 3 Example 19.1 9.2 1.75 Example 4 Example 2 5.8 7.6 1.71 Comparative Commercial11.0 0.4 2.08 Example 5 composite hydroxide

<Evaluation of Battery Properties>

(1) Fabrication of a Lithium Secondary Battery

A positive electrode mixture was prepared by mixing together 85% by massof each of the lithium nickel manganese cobalt composite oxides obtainedin Examples 3 and 4 and Comparative Example 5, 10% by mass of a graphitepowder and 5% by mass of polyvinylidene fluoride, and the obtainedmixture was dispersed in N-methyl-2-pyrrolidinone to prepare a kneadedpaste. An aluminum foil was coated with the obtained kneaded paste, thendried, and punched out by press working to form a disc of mm indiameter, and thus a positive electrode plate was obtained.

Next, a lithium secondary battery was fabricated by using the positiveelectrode plate, and by using the individual members such as aseparator, a negative electrode, a positive electrode, current collectorplates, mounting brackets, external terminals and an electrolyte. Amongthese members, the negative electrode used was a lithium metal foil, andthe electrolyte used was an electrolyte prepared by dissolving 1 mol ofLiPF₆ in 1 liter of a one-to-one kneaded liquid of ethylene carbonateand methyl ethyl carbonate.

(2) Evaluation of Battery Performance

Each of the fabricated lithium secondary batteries was operated at roomtemperature to evaluate the initial discharge capacity, the initialcharge-discharge efficiency and the load property, and the results thusobtained are shown in Table 3.

<Evaluation Methods of Initial Discharge Capacity and InitialCharge-Discharge Efficiency>

Charge-discharge was conducted as follows: under the condition of theconstant-current and constant-voltage (CCCV) in relation to the positiveelectrode, charge was conducted at 1.0 C over a period of 5 hours up to4.3 V, and thereafter, discharge was conducted at a discharge rate of0.2 C down to 2.7 V. The initial discharge capacity and the initialcharge-discharge efficiency were measured. The results thus obtained areshown in Table 3. It is to be noted that the initial charge-dischargeefficiency was obtained on the basis of the following calculationformula:Initial charge-discharge efficiency (%)=[(initial dischargecapacity)/(initial charge capacity)]×100

<Evaluation of Load Property>

Each of the fabricated lithium secondary batteries was operated at roomtemperature to evaluate the load property. First, charge-discharge wasconducted as follows: under the condition of the constant-current andconstant-voltage (CCCV) in relation to the positive electrode, chargewas conducted at 0.5 C over a period of 5 hours up to 4.3 V, andthereafter, discharge was conducted at a discharge rate of 0.2 C down to2.7 V. A set of these operations was defined as one cycle. Every cycle,the discharge capacity was measured. This cycle was repeated threetimes, and the arithmetic average of the three discharge capacity valueswas derived to be defined as the discharge capacity at 0.2 C.

The above-described operation was also conducted at 2 C to obtain adischarge capacity. From these two discharge capacity values, thedischarge capacity ratio of the discharge capacity at 2 C to thedischarge capacity at 0.2 C was calculated. The results thus obtainedare also shown in Table 3 under the heading of load property. The largerthis discharge capacity ratio is, the better the load property.

TABLE 3 Initial Initial charge- discharge discharge capacity efficiencyLoad (mAh/g) (%) property Example 3 166 94 0.88 Example 4 169 93 0.90Comparative 153 70 0.79 Example 5

1. A composite carbonate comprising nickel atoms, manganese atoms andcobalt atoms, and having an average particle size of 5 μm or more andless than 20 μm, a BET specific surface area of 40 to 80 m²/g and a tapdensity of 1.7 g/ml or more.
 2. The composite carbonate according toclaim 1, wherein the molar ratio of the nickel atom content to manganeseatom content Ni:Mn is 1:0.5 to 2.0, and wherein the molar ratio of thenickel atom content to cobalt atom content Ni:Co is 1:0.5 to 2.0.